A overrated and useless battle formation given too much importance in TV serials and popular fictions based on the Mahabharata.
This chakravyuha did not help the Kauravas or the Pandavas in any instance, it was easily a handicap and caused more harm to the Kuru army than good.
It means: “any circular array of troops” Sanskrit Dictionary for Spoken Sanskrit
Drona claimed that this formation couldnt be penetrated by even gods:
“Today I will also form an array that impenetrable by the very gods.”
Here is its description:
“On the other hand, the array formed by Drona, O king, looked resplendent. Indeed, that array was incapable of being looked at like the sun himself when in his course he reaches the meridian and scorches (everything underneath).”
It was described as a formation which could not be gazed/stared upon. Somehow it was invisible to the human eye.
Why yudhishthir ordered Abhimanyu:
“Beholding Drona advancing in rage. Yudhishthira thought of diverse means for checking his progress. At last, regarding Drona incapable of being resisted by any one else, Yudhishthira placed that heavy and unbearable burden on the son of Subhadra.”
The son of Subhadra is Abhimanyu, it was believed by Yudhisthir that no one else could check Drona besides Abhimanyu.
Here is the plan of Yudhishthir -
"Yudhishthira said, 'Break this array once, O foremost of warriors, and make a passage for us. All of us will follow thee in the track by which thou wilt go. In battle, thou art equal to Dhananjaya himself. Seeing thee enter, we shall follow thee, protecting thee on all sides.'
Here is the plan of Bhima -
"Bhima said, 'I myself will follow thee, and Dhrishtadyumna and Satyaki, and the Panchalas, and the Prabhadrakas. After the array once is broken by thee, will enter it repeatedly and slay the foremost warriors within it.'
They wanted Abhimanyu to break the Chakravyuha then make a pathway for them, to enter after him and then protect him.
The plan was foiled by Jayadratha but in the end it didn’t do anything well for the Kauravas, they killed one warrior (Abhimanyu) yet lost more than 25 percent of their army (which would be millions of warriors).
“The boy of mighty arms having penetrated the impenetrable array, shall range within it fearlessly and send a fourth part of the hostile force, in course of half a day, unto the regions of the king of the dead.”
I call this formation (Chakravyuha) useless because of how much the Kauravas lost just to kill one man. What happened? What did they gain? They only lost. This is no victory its another defeat.